An ideal gas is defined as a gas in which the molecules can be considered as "point masses" thereby taking up negligible volume compared to the volume of the container. No significant forces, intermolecular interactions, exist between the molecules except during collisions which are considered to be perfectly elastic. All real gases that are far removed from conditions at which they condense, low temperatures or high pressures, display nearly ideal behavior.

Avagadro's Number:NA = 6.022 x 1023

The number of carbon atoms in 12 grams of a sample of carbon-12 is called
Avogadro's number, NA,
which equals
6.022 x 1023 molecules. A mole of any substance contains Avagadro's number of particles.

Ideal Gas Law:PV = nRT

where

P is the pressure measured in Pa = N/m2 (1 atm = 1.013 x 105 Pa)

V is the volume measured in m3

n is the amount of gas present measured in moles

T is the temperature measured in K

R is the ideal gas law constant: 8.314 J/mole K (0.0821 atm L/mole K)

Combined Gas Law:

where

P1, V1, n1 and T1 are the initial values

P2, V2, n2 and T2 are the final values

When selected quantities are held constant then this law can be restated as three others.

Boyle's Law

temperature and the amount of gas presentheld constant

Charles' Law

pressure and the amount of gas presentheld constant

Guy-Lussac's Law

volume and the amount of gas presentheld constant

Some fundamental relationships

Often in determining the amount of gas present in moles (n), you need be familiar with the following relationships between Avogadro's number (NA), the amount of mass present (m), molecular mass (N), and the mass of a single molecule ().